1. Field of the Invention
This invention relates to an improved method to obtain color image by a process with a monobath developing intensifying solution. More particularly this invention relates to a method to obtain color image by processing silver halide photographic material having photographic couplers and small content of silver halide--that is low silver containing photographic material--in a monobath developing intensifying solution containing both H.sub.2 O.sub.2 or compounds which can release H.sub.2 O.sub.2 and a color developing agent.
2. Description of the Prior Art
It is well known that there are many methods to intensify a image by processing with some reagents, after a development of silver halide photosensitive material.
It is described, for example, in the "History of Color Photography" 2nd Ed. 406p (1956), written by Friedman, that in the presence of a coupler, a paraphenylenediamine color developing agent is oxidized by the decomposition of H.sub.2 O.sub.2 on the surface of a catalyst followed by coupling reaction of said oxidized agent with the coupler to form a dye. And, other photographic methods utilizing the decomposition of H.sub.2 O.sub.2 on the surface of noble metals are described in applications in West Germany (OLS) Nos. 1,813,920, 1,950,102, 1,961,029, 2,044,833, 2,044,993, 2,056,360, 2,056,359 and 2,120,091 respectively.
On the otherhand, color intensifying methods employing cobalt complex salt on the surface of noble metals are described, in several issues of the Japanese Patent Gazette under Provisional Publication Nos. 9,728/73, 9,729/73, 48,130/73, 84,229/74, 84,240/74, 97,614/74, 102,340/74 and 102,314/74, which laid "open to public inspection" (hereinafter "Japanese Patent Application--OPI" in this description).
The methods of color intensification using halogenous acids, such as chlorous acid are described in Japanese Patent Application--OPI Nos. 53,826/76 and 13,335/77. A color intensifying method with iodoso compounds, such as iodosobenzoic acid, is mentioned in Japanese Patent Application--OPI No. 73,731/77.
These compounds such as peroxides, halogenous acids, iodoso compounds and cobalt complex salts (III), which have an intensifying effect, are called intensifying agents and the treating bath which includes intensifying agent is called as intensifying bath.
Image intensifying techniques using peroxides or cobalt (III) complex salts as catalysts are especially well known as typical techniques for image intensification. It is considered that the intensification with peroxide gives the largest amplification factor.
Above described methods are known as ways to intensify an image with an oxidation product of a color developing agent. The oxidation product of a color developing agent is produced by a redox reaction between an intensifying agent and a color developing agent, then it forms color images of high density. The redox reaction occurs on a developed silver specks (a catalyst of this reaction) which have grown from the latent image specks which are formed by an imagewise exposure on a silver halide photographic material.
In other words, the intensifying process is comprised of several processes. For example, one process is to dip color photographic materials in a intensifying bath after color development. Another process is to dip color photographic materials which have been developed with a black and white developing solution into a color developing solution, and then dip into an intensifying bath. This total process is comprised of
(1) a procedure to improve latent image by development and
(2) a procedure to intensify image in a intensifying bath utilizing redox reactions on developed silver specks which occur between intensifying agents and color developers which had been retained in layers of photographic film.
All of these procedures are generally known as intensifying process.
Therefore, in order to intensify an image with high efficiency, a large amount of developing agent should be retained in a layer of the photographic material. Moreover, before the developing agent diffuses into the intensifying bath it should be quickly oxidized by the intensifying agent (in this oxdization the silver speck acts as a catalyst).
In this point of view, specific methods employing developing agents having large oilphilicity into developing solution were disclosed in U.S. Pat. No. 3,816,134 and in Japanese Patent Application--OPI No. 30,333/78.
The fog which may be formed in the intensification process can be suppressed, without degrading the activity of catalytic specks, using techniques which were disclosed in Japanese Patent Application--OPI Nos. 13,335/77 and 19,829/78.
As above described, many techniques in relation to the intensifying process have been developed. The intensification method, however, may not be desirable because the processing steps can not be simplified as compared to the presently existing methods. In intensification process increases the processing steps because of the intensifying bath; thereby spoiling the simplicity of the total process. The simplification of the steps was disclosed in U.S. Pat. Nos. 3,847,619 and 3,923,511. These patents disclose that the development process, the intensification process and the bleaching process may be carried out in a monobath with cobalt (III) complex. However, it is difficult to obtain excellent color image in cases in which a low silver containing photographic material is processed in a monobath developing intensifying solution containing cobalt (III) complex. In this process the result is that fog is caused by the intensification and the image is of low density.
Furthermore, it is mentioned in West Germany Patent No. 1,813,920 and in Japanese Patent Application--OPI Nos. 13,335/77, 127,555/80 etc., that it is possible to make both development and intensification in one bath containing H.sub.2 O.sub.2 which results in a large amplifying efficiency. However, when a low silver containing photographic material is used, even if H.sub.2 O.sub.2 is added into a conventional color developing solution, KBr (usually several hundreds mg/l of KBr is added in the color developer) existing in the color developing solution spoils the image and the expected effect from the monobath developing intensifying process can not be obtained.
The method to solve these problems existing in a conventional processes is given in Japanese Patent Application No. 117,973/81 (which is laid open; Japanese Patent Application--OPI No. 18,629/83). That method, with small numbers of processing step, can intensify the image without fog and give a large amplification efficiency even if a low silver containing color photographic material is used. In more detail, that invention is the method to form color images by processing imagewisely irradiated photographic material under the existence of compounds which can react with or adsorb on silver halide, using monobath developing intensifying solution which contains neither Br.sup.- nor I.sup.- substantially but contains both H.sub.2 O.sub.2 or chemicals which can release H.sub.2 O.sub.2 and color developing agents.
In that process, the quantity of the color developing agent to be added is at least 10.sup.-3 mole/l and preferably 2.times.10.sup.-3 .about.10.sup.-1 mole/l, and the quantity of H.sub.2 O.sub.2 against the color developing agent is 0.5.about.200 (mole/mole) and preferably 1.about.80 (mole/mole), in addition, it is preferable that Br.sup.- and I.sup.- are not contained, however, they may be present in an amount such as 2.times.10.sup.-4 mole/l.
Although the above process has the effect of saving large amounts of silver, that technique is not sufficient in following points: first, the monobath developing intensifying solution is not stable and has a limited shelf life. Moreover it is impossible to reproduce good images when only a small amount of the solution is replenished. The conventional color developing process does not have this defect; secondary, if a large amount of the solution is replenished to get a sufficiently reproduced image, total cost will increase; for example, because of the expense incurred in resulting the waste solution.
Those problems are not solved by the process which abandons the treating solution every time. Because, that process results in a decrease of quantity of the developing intensifying solution per unit area of photosensitive material to be developed, that is, after a little increase of halogen ions such as Br.sup.- and I.sup.-, which have dissolved from the photosensitive material into the developing intensifying solution, the solution is spoiled markedly and image with only low density can be obtained.
On the other hand, it is known that a spoiled color developer can be refreshed by contacting it to anion exchanger as disclosed, for example, in West Germany Patent No. 2,717,674, U.S. Pat. No. 3,253,920, Japanese Patent Application--OPI Nos. 37,731/79 and 1,048/81 etc. But in that case, as the quantity of halide ions (especially Br.sup.- and I.sup.-) in the color developer is required to be constant, though it is troublesome, some technique should be introduced to control the concentration of halide ions.
In a known process to reproduce spoiled color developer using anion exchanger, products of oxidized developing agents accumulate in the color developer. In this case ion exchange ability of said anion exchanger is remarkably damaged even when a small amount of spoiled color developer is passed through it. So, above mentioned techniques have the deficiency that said spoiled color developer should be in contact with absorbents, before it is in contact with anion exchanger (Japanese Patent Application--OPI No. 132,343/78 etc.).